With good speech you can talk him out of it though he'll for the assassination of Westong job onto you (regardless of wether you have the case or not).
This can be interesting if you opened the case and screwed up that quest, but I only managed to do this once and don't know the full requirements to acheive that.
So well, otherwise, sneak, or like I do, RUN. I've had more luck with running directly to the stairs then with sneaking personally.